The concept of a hybrid lasers with an intracavity wavelength stabilizing components has been established in the prior art. A hybrid is understood as a laser consisting of one active medium of one type and a second medium, of which the state of the matter or composition is different from the first medium. Such a hybrid may provide an additional gain or loss of photons of a specific wavelength. Passive and active embodiments of such inventions exist. In early inventions, the methane gas or iodine vapor cells were used to control the lock of the wavelengths in He—Ne lasers. U.S. Pat. No. 3,718,868 is representative of such implementations.
In other embodiments, the concept was employed in detecting the Laser Induced Fluorescence (LIF) spectrum of a suitable medium in a reference cell with a wavelength tuning mechanism, for example see U.S. Pat. No. 5,390,203. Other solutions include laser wavelength control through opto-galvanic effects, which is in a feedback control loop with the laser, such as disclosed in U.S. Pat. No. 4,932,030. All of those methods require some type of an electro-optic, opto-, or servo-mechanism to tune wavelengths and lock to the atomic transition. Another method is to use the oscillator-amplifier configurations to control the wavelength as disclosed in U.S. Pat. No. 3,919,664. This occurs when the weak laser of a well-established and stable wavelength acts as an oscillator and forces the high power gain laser medium to operate at the same wavelength. The oscillator and amplifier media can be heterogeneous i.e. employing different active media. The injection seeding is one of a possibility of subsets in such lasers, such as disclosed in U.S. Pat. No. 4,918,704.
There is a need for lasers with output beams of predetermined and stable wavelengths and in resonance with atomic transitions of elements terminated in ground or metastable states. Notably, this is seen in the sodium laser used in astronomy. In general, such lasers operating at atomic fluorescence resonance wavelengths have the potential to be used in many applications such as: interferometry, metrology, optical pumping to generate THz radiation, analytical chemistry, Raman spectroscopy, fiber optics gyroscopes, plasma diagnostics and others.
For example, lasers that resonantly probe or pump ground states or metastable states of atoms in a gas phase are of particular importance for applications in analytical chemistry, atomic clocks, plasma cleaning, plasma diagnostics, artificial stars for astronomy, and pumping alkali metal atomic vapors. Wavelength tunable dye lasers (Vol. 16, No. 1, Applied Physics Letters, p. 3, January 1970) and laser diodes (Vol. 17, Issue 1, IEEE Journal of Quantum Electronics, p. 44, January 1981.) are two examples.
Lasers with intracavity, wavelength-stabilizing components have been established in the prior art. In early inventions methane gas or iodine vapor cells were used to control the lock of the wavelengths in He—Ne lasers, for example as disclosed in U.S. Pat. No. 3,718,868. However, wavelengths were not resonant (coupled to ground states) to transitions in atomic vapors. In other inventions, such as disclosed in U.S. Pat. No. 5,390,203, a wavelength tuning mechanism is used to detect the Laser Induced Fluorescence (LIF) spectrum of a suitable medium in a reference cell. Other inventions employed opto-galvanic devices, such as disclosed in U.S. Pat. No. 4,932,030, in feedback control loops. Another method utilized an oscillator-amplifier configuration is disclosed in U.S. Pat. No. 3,919,664. A weak laser of a well-established and stable wavelength acts as an oscillator and forces the high power gain laser medium to operate at the same wavelength. Injection seeding is another method of achieving wavelength locking, which is disclosed in U.S. Pat. No. 4,918,704. A simpler construction, with the lack of complex servo-loops to control wavelengths, and the low cost of components would be an obvious advantage and benefit to the optical technologies field.
In US Patent Application Publication US2009/0059980 A1 entitled “High Stability Frequency Reference Based on Self-locked Alkali-Vapor Laser” issuing to Braun et al on Mar. 5, 2009, is disclosed a VCSEL optical gain element. It uses a photonics system comprising of an optical gain element, VCSEL diode with its emission band centered at the atomic absorption band to the atomic vapor contained inside a cavity. Such a system requires a precisely engineered VCSEL with a preset and narrow optical wavelength, which imposes tight tolerances in semiconductor process to make such a chip. In addition, there is a disadvantage in that a resonator cavity length must be in an active feedback loop with secondary electronics.
One of the paths in simplifying the laser system would be to provide a sufficiently broad active gain medium, with low constraints for positioning of its gain profile in respect to desired atomic transition. Gain mediums such as a semiconductor solid state laser, a dye laser, or materials in fiber optics lasers are fit for such a purpose. In such embodiments a strong radiative coupling between spontaneous emission from a non-coherent atomic plasma source, contained inside the resonator cavity would seed the photons desired to initiate the wavelength lock. However, a phenomenon known as amplified spontaneous emission (ASE) has not been utilized in atomic lasers or turned into practical implementations. ASE plays only a parasitic role in the lasers having a high gain active medium, thus degrading wanted directional laser action, and adversely affecting wavelength stability and output power. ASE may also cause lasing in random free run mode.
There are inventions addressing these types of problems, for example, U.S. Pat. No. 8,268,649. A significant amount of theoretical and experimental work has addressed the role of Rabi oscillations in wavelength self-locking in two level atomic systems. The theoretical and experimental work of Kroon (J. P. C. Kroon, et al. in Phys. Review A Vol. 31, Number 6, June 1985, p3724) shows some level of amplification in the upper state of populated neon atoms in optical-pumping experiments. However, spontaneous decay, due to sensitivity of pumping geometries, prevented the observations of Rabi oscillations in continuous mode of operation. In the work of Bagaev (Bagaev, S. N. et al., Opt. Spectrosc. USSR 94, 2003, 1, 92-98, “An Experimental and Theoretical Study of the Two-Wave Interactions [of a probe wave and of a pumping wave] of Wide-band Multimode Laser Pulses With an Optically Dense Extended Resonant Medium”), the authors observed strong amplification of two wave pumping experiments. Neither of those two cited works led to the development of a laser device of desired self-locking characteristics.
There are other atomic emission line lasers that operate on a three level system such as disclosed in U.S. Pat. No. 6,643,311 entitled “Diode-Pumped Alkali Laser” and issuing to Krupke on Nov. 4, 2003. Therein disclosed is a laser pumped by a laser diode array, where the pumped laser gain medium comprises an atomic vapor of an alkali element buffered with a mixture of rare-gas and selected molecular gases.
None of these prior lasers provide a relatively simple and stable laser that can produce an atomic emission wavelength that is passively locked and of high power in a compact design. Therefore, the is a need for a hybrid laser of simple construction that is compact and that can provide a high powered output laser of a determined atomic emission wavelength.